Congestive heart failure is a complex and heterogeneous disease state associated with decreased cardiac performance and increased pulmonary and peripheral oedema. Congestive heart failure results when the left, right or both ventricles fail to pump sufficient blood to meet the body's needs. An estimated 4 million people currently in the United States have congestive heart failure. While no single drug or drug class has proven to be ideal in treating this disease, vasodilator therapy constitutes a major approach in its clinical management.
Organic nitrate esters, such as nitroglycerin, isosorbide dinitrate, isosorbide-5-mononitrate, etc. are organic chemicals that contain the ONO.sub.2 group. Nitrates are part of a family of vasodilators called nitrovasodilators and have enjoyed extensive use in cardiovascular therapy; but other members of this class, e.g., nitroprusside, molsidomine and organic nitrites are not organic nitrates. Nitrovasodilators such as isosorbide dinitrate and glyceryl trinitrate are useful in treating congestive heart failure because they cause a prompt reduction in preload and/or afterload, and relieve the venous congestion often associated with this disease.
Nitroglycerin, also referred to as trinitroglycerin or glycerin trinitrate, has also been used to treat angina pectoris for over 100 years. Nitroglycerin and other nitrovasodilators have been available for the treatment of angina pectoris and congestive heart failure in a number of different dosage forms for some time. These include sublingual, oral and buccal tablets as well as capsules, topical creams and ointments, patches, tapes, lingual sprays and intravenous solutions.
Transdermal nitroglycerin patches were introduced in recent years in an effort to overcome some of the disadvantages and inconveniences of other dosage forms. In particular, transdermal patches were formulated to provide increased systemic bioavailability as well as constant delivery of the drug over a 24 hour period or longer. Typically, the patches are applied once daily, either in the morning or evening, and changed daily at approximately the same time, and have become popular in the treatment of chronic, stable angina and congestive heart failure.
However, the positive effects of these patches are often short lived. For example, it has been shown that nitroglycerin produces rapid hemodynamic tolerance (within several hours) in congestive heart failure after continuous administration either by intravenous or transdermal routes. Intermittent dosing with a regimen of 12 hours on/12 hours off can avoid development of tolerance but the effect of the previous dose is lost within 2 hours of drug withdrawal, leaving the patient unprotected during the majority of the "dose-off" period. Furthermore, a more frequent on/off dosing strategy (4 or 8 hour on/off cycles) was not successful in avoiding tolerance development. At present no dosage regimen with nitrovasodilators has been developed that can achieve the dual objectives of avoidance of hemodynamic tolerance while continuously maintaining their beneficial effects.
Additionally, headaches typically accompany treatment with organic nitrates such as nitroglycerin. Headaches may be recurring with each daily dose, especially at higher doses. Aside from headaches, which may be severe and persistent, other adverse central nervous system (CNS) reactions include apprehension, restlessness, weakness, vertigo, dizziness and faintness.